1. Field of the Invention
The present invention relates to a mobile communication system, and more particularly to a method for managing carriers allocated to a mobile station (MS) in a broadband wireless access system supporting multiple carriers, and an apparatus for the method.
2. Discussion of the Related Art
A brief description of carriers will be given hereinbelow.
A user may perform modulation on the amplitude, frequency, and/or phase of a sine wave or a periodic pulse wave to include information which is desired to be transmitted. At this time, the sine wave or pulse wave serving to convey information is called a carrier.
Methods for modulating a carrier include a single-carrier modulation (SCM) scheme and a multi-carrier modulation (MCM) scheme. The SCM scheme performs modulation such that all information is carried on a single carrier.
The MCM scheme divides an entire bandwidth channel of one carrier into subchannels having multiple narrow bandwidths and transmits multiple narrowband subcarriers through respective subchannels.
When using the MCM scheme, each subchannel may approximate to a flat channel due to a narrow bandwidth. A user may compensate for distortion of a channel using a simple equalizer. The MCM scheme may be implemented at a high speed using Fast Fourier Transform (FFT). Namely, the MCM scheme is favorable during high-rate data transmission as compared to the SCM scheme.
As the capabilities of a base station and/or a terminal have been developed, a frequency bandwidth which can be provided or used by the base station and/or the terminal has been enlarged. Accordingly, in the embodiments of the present invention, a multi-carrier system supporting broadband by aggregating one or more carriers is proposed.
Specifically, the multi-carrier system, which will be described hereafter, uses carriers by aggregating one or more carriers, unlike the afore-mentioned MCM scheme which uses carriers by segregating one carrier.
To efficiently use multiple bands or multiple carriers, a technique in which one medium access control (MAC) entity manages multiple carriers (e.g., multiple frequency carriers) has been proposed.
FIGS. 1(a) and 1(b) illustrate methods for transmitting and receiving signals based on a multi-band radio frequency (RF) scheme.
In FIGS. 1(a) and 1(b), one MAC layer in each of a transmitting end and a receiving end may manage multiple carriers to efficiently use the multiple carriers. To effectively transmit and receive the multiple carriers, it is assumed that both the transmitting end and the receiving end can transmit and receive the multiple carriers. Since frequency carriers managed by one MAC layer do not need to be contiguous, the above method enables flexible resource management. More specifically, the frequency carriers may have contiguous aggregation or non-contiguous aggregation.
In FIGS. 1(a) and 1(b), physical layers (PHY 0, PHY 1, . . . , PHY n-2, and PHYn-1) represent multiple bands and each of the bands may have a frequency carrier (FC) size allocated for a specific service according to a predetermined frequency policy. For example, PHY 0 (RF carrier 0) may have a frequency band size allocated for a general FM radio broadcast and PHY 1 (RF carrier 1) may have a frequency band size allocated for cellular phone communication.
Although each frequency band may have a different FA size depending on the characteristics thereof, it is assumed in the following description that each frequency carrier (FC) has a size of A MHz for convenience of explanation. Each frequency allocation (FA) band may be represented by a carrier frequency that enables a baseband signal to be used in each frequency band. Thus, in the following description, each FA will be referred to as a “carrier frequency band” or will simply be referred to as a “carrier” representing each carrier frequency band unless such use causes confusion. As in the recent 3rd generation partnership project (3GPP) long term evolution-advanced (LTE-A), the carrier may also be referred to as a “component carrier” to discriminate it from a subcarrier used in the multi-carrier system.
As such, the “multi-band” scheme may also be referred to as a “multi-carrier” scheme or a “carrier aggregation” scheme.
FIG. 2 is a view showing an example of the use of multiple carriers in a general wireless communication system.
The multiple carriers of general technology may employ contiguous carrier aggregation as shown in FIG. 2(a) or non-contiguous carrier aggregation as shown in FIG. 2(b). The combination unit of such carriers is a basic bandwidth unit of a general legacy system (e.g., Long Term Evolution (LTE) in an LTE-advanced system or IEEE 802.16e in an IEEE 802.16m system). In a multi-carrier environment of general technology, two types of carriers are defined as follows.
First, a first carrier (also called a primary carrier) is the carrier used by a Base Station (BS) and a Mobile Station (MS) to exchange traffic and full PHY/MAC control information defined in the 16 m specification. Further, the primary carrier is used for control functions for proper MS operation, such as network entry. Each MS shall have only one primary carrier per cell.
A second carrier (also called a secondary carrier) is an additional carrier which the MS may use for traffic exchange, only per BS's specific allocation commands and rules, typically received on the primary carrier. The secondary carrier may also include control signaling to support multi-carrier operation.
In the general technology, the carriers of a multi-carrier system based on the above-described primary and secondary carriers may be classified into a fully configured carrier and a partially configured carrier.
First, the fully configured carrier is a carrier for which all control signaling actions including synchronization, broadcast, multicast and unicast control channels are configured. Further, information and parameters regarding multi-carrier operation and the other carriers can also be included in the control channels.
The partially configured carrier is a carrier in which all control channels for supporting downlink (DL) transmission in a downlink carrier other than an uplink carrier during Time Division Duplexing (TDD) DL transmission or in Frequency Division Duplexing (FDD) mode are configured.
Generally, an MS may perform initial network entry through a primary carrier, and may exchange mutual multi-carrier capability information in a registration process for exchanging an Advanced Air Interface (AAI) registration request response (AAI_REG-REQ/RSP) message with a BS.
Therefore, the MS acquires information of available carrier(s) of the BS, and the MS can allocate at least one available secondary carrier to the MS. Prior to performing data exchange through the allocated carrier, the corresponding carrier must be activated. However, the carrier activation procedure has yet to be defined in the current standard.